Consolidation

The production of fiber reinforced thermoplastic structures generally involves multiple (and often different) processing steps. As an example, the manufacturing process of a stiffened panel might involve a pre-consolidation step for flat blanks followed by a press-forming step to manufacture the stiffeners. Subsequently, these stiffeners can be joined to a fiber-placed skin by co-consolidation.

Background/Introduction

The production of fiber reinforced thermoplastic structures generally involves multiple (and often different) processing steps. As an example, the manufacturing process of a stiffened panel might involve a pre-consolidation step for flat blanks followed by a press-forming step to manufacture the stiffeners. Subsequently, these stiffeners can be joined to a fiber-placed skin by co-consolidation. The thermoplastic composite material is repeatedly heated, cooled and pressurized during all these consecutive processing steps. As the performance of thermoplastic composites depends strongly on the processing history, all these different steps influence the performance of the final structure. Therefore, proper process optimization (in terms of efficiency and robustness) can only take place if the complete processing chain is taken into account. Within this project, the physical mechanisms underlying the consolidation of thermoplastic composites are investigated and subsequently guidelines will be formulated for multi-step processing.

Approach

The mechanisms governing the consolidation of thermoplastic composites are identified by means of experiments and described using elementary model equations. The mechanisms of interest include for example, void collapse, interlaminar bonding, fiber compaction, crystallization and degradation. Well-established models from literature will be used when deemed adequate, while new approaches will be explored when this is not the case. As an example, a void collapse model based on the diffusion of gasses and volatiles through the polymer matrix was developed to predict porosity as a function of the pressure and temperature history. The required material property data for the identified mechanism will be obtained experimentally for a selection of materials. Finally, the elementary model equations are integrated in a process design tool, which will be used to derive processing and material guidelines for multi-step consolidation of thermoplastic composite materials.

TPRC, the ThermoPlastic composites Research Center in the Netherlands, is an open innovation, research- and development center that aims for thermoplastic composites for a broad range of end use markets.